Production of dry ice from natural gas



April 0, 1951 R. P. RUSSELL ETAL 2,548,498

PRODUCTION OF DRY ICE FROM NATURAL GAS Filed Feb. 17, 1948ZQACpILLiiATION i GAS (25 5 c 'FlzAqfloN 49 L 5 SgPAQM-QIL 2 EPAIZATOR(0 5 45 SULFUR l -27 2 & EMOVAL 4 L l-EACH; c 5 5 28 31 1 54 l CDRYEK Z7l 3-, EQTQAQTIQN QEEYCLE :5: TOM/Ek- 5:1 @UQIF D C l GAS VENT 50 52 53 QI ZDIZY 1c? Cdc'zlfer H. Zupp BOA/waters I 5* Patented Apr. 10, 1951UNITED STATES PATENT OFFICE" 2,548,498 PRODUCTION OF DRY ICE FROMNATURAL GAS Robert. P. Russell and Walter H; Rupp, Mountainside, N..I'.,, assignors to Standard Oil Development: Company, a corporation ofDelaware Application February 17, 1948, Serial No. 8,767 4 Claims. (01.62-170) 1 v This invention relates to the production of Referring to thedrawing, I designates a ga or solid carbon dioxide from raw natural gasconoil well such as is encountered in the. search for taining gaseous toheavy crude oil hydrocarbons. petroleum. The fluids from well I arewithdrawn In accordance with the invention, the well fluid from the wellthrough line 2, and are introduced of a petroleum well is separated intoa gas cut 5 to separator 3, wherein the normally liquid fracofsubstantially fixed gases and methane, an tions are separated from thenormally gaseous. ethane cut, and a C3 and heavier hydrocarbon Crude oilis withdrawn from the bottom of sepacut. The fixed gas and methane outis burned rator 3; through line 4, and the gaseous fractions withsubstantially pure oxygen to form carbon are Withdrawn overhead throughline 5. The dioxide. The ethane cut is then used in a liquid gaseousfractions so withdrawn may be subjected phase process to purify the C02.The purified to fractionation in a conventional casinghead carbondioxide is then sublimed and pressed to recovery plant or equivalentrefinery plant equipform solid carbon dioxide, or Dry-Ice. mentindicated by the numeral 6. The most t th present t carbon dioxide in thform volatile fraction obtained from fractionation zone known as Dry Iceis becoming increasingly im- 6' comprises me ha e, hy ro and fixedgases, portant as a refrigerant. In this capacity it is Which y be w hwn hr h line 1. The principally d in th preservation of foods As leastvolatile fraction comprises C3 hydrocarbons a result of the directcontact of the carbon and heavier hydrocarbons W h may be Withdioxidewith food stufis, it is essential that the drawn as a o s product t o hline 8- The Dry Ice employed as a refrigerant be of exceedintermediatefraction comprises .02 hydrocarbons ingly high purity; It is necessarythat the Dry which are withdrawn through line 9. 'AS indi- Igce becolorless, odorless, tasteless, and non-toxic. Gated, Suitable methodsvfor securing the frac- For this reason the initial purity of the carbontionation of the C1, C2 and C3 hydrocarbons are dioxide and thepurification of the carbon dioxide Well known As diagrammatically i srated in us d in th preparation of Dry Ice is Very i the drawings, thisfractionation may convenientportant. ly be conducted in a fractionationzone 6 pro- At the present time carbon dioxide used in the Vided with alar e number o hor n a y disproduction of Dry Ice is obtained fromcarbon p s d, v t a ly spa d u l ap fraetionatine dioxide rich naturalgases, as a by-product' of v plates r e r equivalent. The C1, C2 and C3fermentation processes, by the combustion of"3'0 hydrocarbons areintroduced to an intermediate v r ou gases, e or 11 fuel or by t pointof the fractionator and the heat requirecomposition of limestone. In allof these cases, ments of the fractionation a p d in any it isnecessaryto subject the carbon dioxide to desired a as or p e, y Wi hd awinvarious purification processes. In particular, it the bottoms pr heatingthe bottoms p o is generally necessary to remove any sulfur comdrecirculating a p t on of the bottoms pounds t, t remove excess t tproduct to the fractionation zone. By virtue of remove heavyhydrocarbonconstituents, Corp the standard 1311110113168 0fdistillation, the fracventionally purification iscarried out by a threetionati'on occurringwill cause a selective progresstep process in whicheach of the above consion of the C1 hydieeai'bens t0 the p of thstituents is extracted by a particular chemical 4o r na i n z n and fthe C3 hy ar ns to reagent. The process is always carried out in thebottom of the fractionation zone. This. will the gas phase. furtherpermit the selective segregation of C2 The present invention dilTersfrom the convenhydrocarbons a t med P s of t e tional processhereinbefore described in that. a fIaCtiOnatOI preferably Partitioned rothe feed novel source of CO2 is employed, yielding carbon inlet y e alfiie s q y. as indidioxide of relatively high concentrationv This cated,a gaseous 1 f a i n m y be Wi hdrawn carbon dioxide is then purified bya liquid phase through line 7, a liquid si'destleain Product processwhich is efi'ective to remove undesirable ti ting C2 hydrocarbons may beWithdrawn odor and taste contaminants and toprovideithe through line 9,and a liquid bottoms product desired purity inaone step process.constituting the C3 hydrocarbons may be with- The invention will be morefully understood drawn from the bottom of: the fractionator. It from thefollowing detailed description in conis pparent tha if desired, severalfractionation nection with the accompanying drawing which stages may beemployed to secure this same obdiagrammatically shows a flow systemembody ng jective. Thus, for example, in a firstfractionathi'sinvention. 55. tion. stage, C: hydrocarbons may beremoved. as

between 1400 to 2500 dioxide and about 15 to nitrogen,

an overhead product while C2 and C3 hydrocarbons may be removed as abottoms product. In the second fractionation stage, the C2 and C3hydrocarbons may then be segregated by causing removal of the C2hydrocarbons as an overhead product and removal of the C3 hydrocarbonsas a bottoms product. In accordance with the present invention the mostvolatile fraction comprising principally methane is withdrawn throughline i, and is introduced to a combustion zone Hi wherein thehydrocarbon constituents are converted to carbon dioxide. The gas sointroduced may, if desired, be compressed in the compressor II to thedesired pressure under which the combustion zone is operated. Oxygen isintroduced to the combustion zone through line |2. It is a particularfeature of the process of this invention that the oxygen used be ofrelatively high purity. As indicated by the drawing, the oxygen systemcomprises an air purification plant wherein air is introduced throughline |3 to a conventional oxygen separation and fractionation plant l4,wherein the air is liquefied to fractionate the oxygen and nitrogen,providing oxygen of about 95-97% purity which may be withdrawn throughline |5. The oxygen plant employed is of conventional design and as itis no part of the present invention, no detailed description is hereinmade as to its nature. The oxygen may be compressed in compressor E6 tothe pressure employed in the combustion zone 50. Combustion zone In isoperated to provide controlled burning of the methane at conditionsranging F., and at a pressure between 0 and 1000 p. s. i., gauge. It ispreferred that a temperature of about 2000 F., and a pressure of about300 to 500 p. s. i., gauge be employed. Cooling tubes 46 are located inthe combustion zone to control the temperature of combustion byvaporizing water introduced in line 41 to form steam which is withdrawnthru line 43. A molal ratio of oxygen to methane of about 2-1 isdesirable, plus a slight excess of oxygen. As described, the methanefraction obtained from fractionation plant 6 from the oxygen plant |4may be recovered under sufiicient pressure to meet the requirements ofthe combustion zone without additional compression. It is for thisreason that compressors H and I6 have The combustion of the methaneusing the high purity oxygen in the combustion zone i0 is carried out toconvert 95-100% of the methane and is effective to provide carbondioxide of relatively high purity which may be readily purified to aproduct suitable for conversion to Dry Ice. The combustion productconsisting of carbon dioxide, water vapor and some unreacted feed gas iswithdrawn from the combustion zone through line H, and is passed tocooler l8, wherein the temperature of the combustion products is droppedto a point sufficient to condense substantially all of the water vaporpresent. This temperature is so chosen that at the conditions ofpressure existing in the combustion zone, and throughout the systemheretofore described, no liquefaction of the carbon dioxide will occur.The cooled stream of gas is then conducted from cooler Hi to separatorI9, wherein the condensed water may be separated from the carbon dioxidegas. Water may be withdrawn through line 20 and the carbon dioxide gasmay be withdrawn overhead through line 2|. The carbon dioxide rich gashas a composition of about 85 to 95% carbon carbon and the oxygenobtained.

been indicated as being optional.

monoxide, and oxygen plus traces of sulfur compounds, water vapor andhydrocarbons. As desired, or necessary, the carbon dioxide may befurther dried in drier 22 which may consist of an alumina, silica gel,or similar type of drier. Compressor 23 may be utilized prior totreatment in the drying tower 22 to supply suflicient pressure so thatcondensation of the CO2 may be brought about in case the combustion zoneH] is operated at a pressure below that desired for liquefaction of theCO2. As stated before, it is not necessary to employ the compressor 23if the gas from the well, through the combustion zone, and the remainderof the process has been maintained at a sufficiently high pressure. Thecarbon dioxide gas from the separator 2|, then, is either passedthrough, or is bypassed the drier 22 and is conducted through line 24 tocooler 25. Cooler 25 may be any desired type of cooler, and mayconveniently be a cold water heat exchanger. It is necessary that thecooler have sufficient capacity to condense sure under which it ismaintained. For example, if the carbon dioxide throughout the system hasbeen held at a pressure of 500 p. s. i., gauge, condensation will occuron cooling to 32 F. similarly if the pressure of the carbon dioxide ismaintained at 1100 p. s. i., gauge, then cooling to F., will besufficient to liqueiy the carbon dioxide. Liquid carbon dioxide iswithdrawn from cooler 25 and is introduced to separator 26 wherein anyuncondensed gas may be removed overhead through line 49. The liquidcarbon dioxide is then withdrawn from separator 25 through line 21.Again, the liquid carbon dioxide may be passed through a drier 28similar to drier 22, or may bypass this drier. Both drier 22 and drier28 are utilized to critically adjust the water content of the carbondioxide. It is desirable to remove all excess water which would have theeffect of freezing valves, causing corrosion, etc. However, a trace ofwater is desirable insofar as a very small proportion of water iseffective in improving the crystalline structure of the final Dry Iceproduct. The liquid carbon dioxide is conducted through line 21 into theextraction tower 29. This tower may have plates, bubble caps, packing,or any of the conventional equipment to secure thorough liquid to liquidmixing. The tower may alternatively consist of a turbo mixer, orequivalent high speed mixing equipment. As illustrated in the drawing,when employing an extraction tower, the liquid carbon dioxide isintroduced to the top of the tower, and flowing downwardly through thetower contacts a stream of liquid C2 hydrocarbons introduced to thebottom of the tower through line 30 which flows upwardly through thetower. Contact of the liquid C2 hydrocarbons with the liquid carbondioxide is carried out at 0 to 80 F. temperature and pressures of300-ll00 p. s. i. g. A preferred range is 32 to 80 R, and 500 to 1100 p.s. i. g. This operation is effective to substantially remove suliurcompounds, traces of water, and heavy oils, rendering the carbon dioxidesubstantially pure. About 10-200% by volume'of the carbon dioxide isrequired to obtain satisfactory purification. The exact percentage willdepend upon the initial impurities of the carbon dioxide. The purecarbon dioxide is withdrawn from the bottom of the extraction towerthrough line 3|, and is conducted to throttling valve 32. This valve isoperated so as to sharply drop the pressure of the liquid carbon dioxideto a point where the carbon dioxide will be converted to the carbondioxide at the pressolid form. A pressure of about 0 to 60 p. s. i. g.is suitable to accomplish this solidification. This pressure reductioncauses the carbon dioxide to cool to such an extent that carbon dioxidesnow is formed. This snow may then be conducted to the conventional typecarbon dioxide press 33, wherein the snow may be compressed to the solidblock form which is known as Dry Ice.

Returning to the extraction tower 29, the C2 hydrocarbons aftercontacting the impure carbon dioxide are withdrawn from the top of thetower through line 3-4. If desired, the impure C2 hydrocarbons maysimply be withdrawn through line 3-3 and may be burned as fuel, or usedfor any other desired purpose. Alternatively, they may be suitablypurified so as to permit recycling in the extraction tower. Thepurification system illustrated comprises two conventional fractionatingzones and 3'! with top refluxing and bottom reboiling. the extractiontower 29 are conducted thru line 59 into the first fractionating zone 36which may be of the reflux type wherein methane, carbon dioxide, andwater vapor may be removed over head through line 38, while C2hydrocarbons and higher are removed as a bottoms product through line39. The bottoms product is then introduced into the second fractionatingzone 31, wherein C2 hydrocarbons are withdrawn overhead through line 49while C3 and heavier hydrocarbons are withdrawn as a bottoms productthrough line 4 l. The bottom fraction comprising heavy oils carries withit substantially all of the impurities removed from the carbon dioxide.Consequently, the C2 fraction withdrawn from the top of the tower issubstantially pure and may be recycled to the extraction tower throughlines 30 and 30. Alternatively, the purified C2 hydrocarbons may bewithdrawn through line 42 and may be used for synthesis purposes, o forany other purpose.

The C2 hydrocarbons employed in the extraction tower initially consistof the C2 fraction of the crude natural gas as obtained from thefractionation plant 6, through line 9. The C2 fraction may be initiallypurified by conducting the liquid hydrocarbons through sulfur removingvessel 43 and drier 4d. equivalent reagents may be employed in vessel 43to remove the sulfur compounds. alumina, florite, silica gel, orequivalent drying agents may be employed in drier i l to dry the C2hydrocarbons. As purified, the C2 fraction may be introduced to line 30through line 45 for utlization in the extraction tower hereinbeforedescribed.

- As described, the present invention relates to an integrated processfor employing the well fluids of a petroleum oil well, or of a naturalgas well to provide carbon dioxide suitable for Dry Ice manufacture. Thewell fluids are fractionated so as to provide separate C1 and C2fractions. The C1 fraction is burned with substantially pure oxygen toprovide carbon dioxide. The C2 fraction is subjected to initialpurification and is then caused to contact the carbon dioxide so as topurify the carbon dioxide sufliciently to provide high quality Dry Ice.A characteristic of this process is the employment of relatively pureoxygen for the combustion of the C1 fraction, whereby the subsequentpurification process is materially simplified. A second characteristicof the process is that the purification of the carbon dioxide is carriedout in the liquid phase The liquid C2 hydrocarbons from Caustic,bauxite, amines, or

Similarly,

6 employing both liquid carbon dioxide and liquid C2 hydrocarbons. Astill further feature is that the entire process may be conducted athigh pressures. Consequently, providing that the source of well fluidsdelivers high pressure constituents, little or no subsequent compressionis required. It will be noted by those skilled in the art that theprocess described is furthermore adaptable to efiicient heat exchange sothat it may be 0perated at a high degree of efiiciency.

Having now fully described the present invention, what is claimed is:

1. The process of producing Dry Ice from pctroleum and natural gas wellfluids, which comprises separating said fluids into at least a C1 and C2fraction, burning said 01 fraction, using oxygen of at least puritytoproduce carbon dioxide, liquefying said carbon dioxide, purifying thesaid C2 fraction, contacting the C2 fraction in liquid phase with theliquefied carbon dioxide fraction, at a pressure of about 300 to 1100pounds per square inch withdrawing liquid carbon dioxide after saidcontact, and sharply dropping the pressure under which the liquid carbondioxide is maintained, whereby evaporation and cooling of the carbondioxide occurs with consequent formation of carbon dioxide snow, andcompressing said carbon dioxide snow.

2. The process defined by claim 1 wherein the C2 fraction, after contactwith the liquid carbon dioxide is fractionated to provide substantiallypure C2 hydrocarbons which are recycled to the said contacting step.

3. The process of claim 1 wherein the C1 fraction is burned at atemperature of about 1400 to 2500 F. at a pressure between 0 to 1000 p.s. i. g.

4. The process of producing Dry Ice from petroleum oil and natural gaswell fluids which comprises separating said fluids into at least a C1and a C2 fraction, burning said C1 fraction at a temperature in. therange of 1400 to 2500 F. and a pressure in the range of 300 to 500 lbs.per square inch, employing oxygen of at least 95% purity to producecarbon dioxide, liquefying said carbon dioxide, purifying the said C2fraction, contacting the liquefied carbon dioxide with 10-200% by volumeof the C2 fraction in liquid phase whereby sulfur compounds and heavyoils are removed from the carbon dioxide, withdrawing the liquid carbondioxide after said contact, and sharply dropping the pressure underwhich the liquid carbon dioxide is maintained, whereby evaporation andcooling of the carbon dioxide occurs with consequent formation ofcarbondioxide snow, and compressing said carbon dioxide snow.

The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name A Date 1,804,432 Pollitzer May 12,1931 1,863,263 Belt June 14, 1932 2,016,815 Gilmore Oct. 8, 19352,039,330 McKee May 5, 1936 FOREIGN PATENTS Number Country Date 263,922Great Britain Jan. 3, 1927

1. THE PROCESS OF PRODUCING DRY ICE FROM PETROLEUM AND NATURAL GAS WELL FLUIDS, WHICH COMPRISES SEPARATING SAID FLUIDS INTO AT LEAST A C1 AND C2 FRACTION, BURNING SAID C1 FRACTION, USING OXYGEN OF AT LEAST 95% PURITY TO PRODUCE CARBON DIOXIDE, LIQUEFYING SAID CARBON DIOXIDE, PURIFYING THE SAID C2 FRACTION, CONTACTING THE C2 FRACTION IN LIQUID PHASE WITH THE LIQUEFIED CARBON DIOXIDE FRACTION, AT A PRESSURE OF ABOUT 300 TO 1100 POUNDS PER SQUARE INCH WITHDRAWING LIQUID CARBON DIOXIDE AFTER SAID CONTACT, AND SHARPLY DROPPING THE PRESSURE UNDER WHICH THE LIQUID CARBON DIOXIDE IS MAINTAINED, WHEREBY EVAPORATION AND COOLING OF THE CARBON DIOXIDE OCCURS WITH CONSEQUENT FORMATION OF CARBON DIOXIDE SNOW, AND COMPRESSING SAID CARBON DIOXIDE SNOW. 